With his job on the line and a growing number of critics calling for his resignation, Shinseki will go before the Veterans Affairs' Committee. The retired decorated Army general will be asked to explain just how the VA's wait-list scandal became such a mess.

Shinseki is likely to be grilled about delays at numerous VA hospitals and a long list of serious problems and allegations of falsifying wait times, many of which were exposed and reported by CNN.

For six months, CNN has been reporting on deadly delays in medical appointments suffered by veterans across the country and veterans who died or were seriously injured while waiting for appointments and care.

The most disturbing and striking problems emerged in Arizona last month as inside sources revealed to CNN details of a secret waiting list for veterans at the Phoenix VA. Charges were leveled that at least 40 American veterans died in Phoenix while waiting for care at the VA there, many of whom were placed on the secret list.

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But even as the Phoenix VA's problems have riveted the nation's attention, numerous whistle-blowers from other VA hospitals across the country have stepped forward in recent weeks. They described similar delays in care for veterans and also varying schemes by officials at those facilities to hide the delays -- in some cases even falsify records or "cook the books."

The secret waiting list in Phoenix was part of an elaborate scheme designed by Veterans Affairs managers there who were trying to hide that 1,400 to 1,600 sick veterans were forced to wait months to see a doctor, according to a recently retired top VA doctor and several high-level sources who spoke exclusively to CNN.

"The scheme was deliberately put in place to avoid the VA's own internal rules," said Dr. Sam Foote, a 24-year Phoenix VA physician who just retired this year and who appeared in an interview for the first time on CNN last month.

The VA requires its hospitals to provide care to patients in a timely manner, typically within 14 to 30 days.

"They [Phoenix VA officials] developed the secret waiting list," said Foote, a respected physician. He told CNN that the elaborate scheme in Phoenix involved shredding evidence to hide the long list of veterans waiting for appointments and care. Foote and the other sources say officials at the VA instructed their staff to not actually make doctor's appointments for veterans within the computer system.

Instead, Foote says, when a veteran is seeking an appointment, "they enter information into the computer and do a screen capture hard copy printout. They then do not save what was put into the computer so there's no record that you were ever here," he said.

According to Foote and the sources, the information was gathered on the secret electronic list and then the information that would show when veterans first began waiting for an appointment was actually destroyed.

"That hard copy, if you will, that has the patient demographic information is then taken and placed onto a secret electronic waiting list, and then the data that is on that paper is shredded," Foote said.

"So the only record that you have ever been there requesting care was on that secret list," he said. "And they wouldn't take you off that secret list until you had an appointment time that was less than 14 days so it would give the appearance that they were improving greatly the waiting times, when in fact they were not."

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Phoenix VA officials denied any knowledge of a secret list, and said they never ordered any staff to hide waiting times. They acknowledged some veterans may have died waiting for care there, but they said they did not have knowledge about why those veterans may have died.

The number of veterans who died recently waiting for care in Phoenix is at least 40, said Foote and the sources. "That's correct. The number's actually higher. ... I would say that 40, there's more than that that I know of, but 40's probably a good number," said Foote.

Thomas Breen, a Navy veteran, was one of those veterans in Phoenix who died, waiting for care on that secret list, according to Foote and several other inside VA sources who spoke to CNN.

As the veteran urinated blood, Breen's son, Teddy Barnes-Breen, and daughter-in-law, Sally, rushed him to the Phoenix VA Emergency room last fall. But they were told they would have to wait for any primary care appointment for him, despite a note indicating an "urgent" need on his chart from ER doctors.

No one called from the VA with a primary care appointment. Sally says she and her father-in-law called "numerous times" in an effort to try to get an urgent appointment for him. She says the response they got was less than helpful.

"Well, you know, we have other patients that are critical as well," Sally says she was told. "It's a seven-month waiting list. And you're gonna have to have patience."

Sally says she kept calling, day after day, from late September to October. She kept up the calls through November. But then she no longer had reason to call.

Thomas Breen died on November 30. The death certificate shows that he died from stage 4 bladder cancer. Months after the initial visit, Sally says she finally did get a call.

"They called me December 6. He's dead already."

"They did not treat him right," said Teddy.

Sally says the VA official told her, "We finally have that appointment. We have a primary for him.' I said, 'Really, you're a little too late, sweetheart.' "

The director of the Phoenix VA, Sharon Helman, was put on administrative leave by Shinseki two weeks ago, along with two of her top aides. But sources inside the VA in Phoenix tell CNN the wait times and problems are still ongoing there.

As a direct result of allegations by Foote and other insiders in Phoenix, investigators from the VA's Inspector General's Office have gone to Phoenix and have been conducting an investigation there for months.

CNN's ongoing investigation into VA health care

But months before revelations of what happened Phoenix came to light, CNN had reported about other veterans who died or were injured while waiting for care at different VA hospitals.

Last summer, CNN started investigating delays in care and appointment wait times at VA facilities across the country.

Since our first report on delays in care at two VA hospitals in Georgia and South Carolina ran in November of 2013, CNN has continued to uncover delays in care at many facilities across the country. Numerous VA staffers have stepped forward to become whistle-blowers and allege dangerously long wait times for veterans and varying efforts to cover them up by officials at the VA.

"I just try to live every day like it's my last day," said Barry Coates, a 44-year-old Gulf War vet who is one of the veterans who has suffered from a delay in care and who spoke to CNN in January.

Coates was having excruciating pain and rectal bleeding in 2011. For a year, the Army veteran went to several VA clinics and hospitals in South Carolina, trying to get help. But the VA's diagnosis was hemorrhoids, and aside from simple pain medication, he was only told he might need a colonoscopy yet not given any appointment for one.

"The problem was getting worse, and I was having more pain," Coates said, talking about one specific VA doctor who he saw every few months. "She again examined me and gave me some prescriptions for other things as far as pain and stuff like that and I noticed again she made another comment -- 'may need colonoscopy.'

"I told her that something needed to be done," said Coates. "But nothing was ever set up ... a consult was never set up. ... I had already been in pain and suffering from this problem for over six months, and it wasn't getting better," Coates said.

When he finally got the appointment, it was still months away.

"I told her that if you were in as much pain as I was and had been going through you wouldn't wait another two months to see what's going on. You would probably do it this week."

Finally about a year after first complaining to his VA doctors of the pain, Coates got a colonoscopy. Doctors discovered a cancerous tumor the size of a baseball -- and the cancer has spread. He is diagnosed with stage 4 cancer that's now in his lungs and liver.

While investigating what happened to Coates, CNN talked to numerous high-level sources inside the VA in Columbia who told CNN that the number of those who died waiting for care just at that hospital could be as high as 20.

Investigators from the VA's Inspector General Office have gone to the VA facilities in Columbia and nearby Augusta, Georgia, to find out whether delays had caused deaths or injuries.

After appearing on CNN, Coates was called to testify at a hearing before the U.S. House Veterans Affairs Committee on April 9, where representatives apologized profusely to him. They expressed astonishment that any veteran could have been treated so badly and had such a delay in care.

On the eve of that congressional hearing, federal VA officials in Washington acknowledged publicly that veterans indeed had died waiting for care -- and not just in Columbia but across the country.

The VA reported 23 veterans had died across the country just from delays in gastrointestinal units. Dozens more veterans were seriously injured from delays in those units, according to the VA. The numbers of dead and injured are likely much higher, numerous inside VA sources have told CNN.

Across the nation, CNN viewers and whistle-blowers respond

CNN has in recent months received thousands of notes, e-mails and viewer tips from veterans or their families detailing similar delays in care they have suffered at VA facilities across the country.

And shortly after revelations from Foote and other inside VA sources about the Phoenix VA problems, whistle-blowers from other VA facilities began to step forward.

Turner says he and other clerks were instructed to simply schedule appointments months in advance while making a note that was the veterans' desired date, even though veterans were seeking immediate help and care.

"What we've been instructed was that -- they are not saying fudged, there is no secret wait list -- but what they've done is come out and just say to us 'zero out that date,' " Turner said.

The "zero," in this case, suggests the patient didn't have to wait at all.

He said it is common for appointments to get "zeroed out" at that VA, essentially hiding wait times. "It could be three months and look like no days (wait)," he added. "It looked like they had scheduled the appointment and got exactly what they wanted," he said.

VA officials in San Antonio say they looked into Turner's allegations and found they were "unsubstantiated." Turner, however, says the local VA officials never even talked to him about the problems, and he today still stands by his statements.

Officials from the VA Inspector General's Office are now on the ground in San Antonio looking into those alleged problems.

"We were told to game the system because it made Cheyenne look good," said Lee, appearing first on CNN.

Lee supplied an e-mail to investigators that was written by another employee in Cheyenne.

The e-mail outlined ways employees could manipulate the system to hide the fact that veterans had to wait months for appointments, said Lee.

The e-mail, obtained by CNN, states: "Yes, it is gaming the system a bit. But you have to know the rules of the game you are playing, and when we exceed the 14-day measure, the front office gets very upset, which doesn't help us. Let me know if this doesn't make sense."

"We were sat down by our supervisor ... and he showed us exactly how to schedule so it looked like it was within that 14-day period," Lee told CNN. "They would keep track of schedulers who were complying and getting 100 percent of that 14 day(s) and those of us who were not," said Lee.

Investigators from the VA's Inspector General are now looking into the allegations there in Cheyenne and Fort Collins as well.

CNN has now confirmed at least a half dozen VA hospitals are under investigation by the VA's Inspector General's Office.

And last week, Shinseki announced he has ordered a "face-to-face audit" at all VA clinics to look into allegations of wait times and possible deaths.

VA: 'We take these allegations very seriously'

Throughout all coverage in recent months, the VA has provided statements to CNN affirming its commitment to veterans' care and good health services, though the Shinseki has refused any interview with CNN.

"We take these allegations very seriously," a statement from Shinseki read. "Based on the request of the independent VA Office of Inspector General, in view of the gravity of the allegations and in the interest of the Inspector General's ability to conduct a thorough and timely review of the Phoenix VA Health Care System (PVAHCS), I have directed that PVAHCS Director Sharon Helman, PVAHCS Associate Director Lance Robinson, and a third PVAHCS employee be placed on administrative leave until further notice."

"Providing veterans the quality care and benefits they have earned through their service is our only mission at the Department of Veterans Affairs. We care deeply for every veteran we are privileged to serve.

"We believe it is important to allow an independent, objective review to proceed. These allegations, if true, are absolutely unacceptable and if the Inspector General's investigation substantiates these claims, swift and appropriate action will be taken.

"Veterans deserve to have full faith in their VA health care. I appreciate the continued hard work and dedication of our employees and of the community stakeholders we work with every day in our service to veterans."

Shinseki vows to get the bottom of the mess and create a more efficient VA that has shorter waits and better care.

But the calls for his resignation are growing, with the American Legion announcing last week he must go. Numerous members of Congress have called for his resignation.